Radio Day is observed on May 7 in Russia, some post-Soviet republics, and Bulgaria, where it is known as Communication Workers' Day or Radio and Television Day. This observance commemorates the invention of radio, which is attributed to various inventors, notably Alexander Popov in Eastern Europe and Guglielmo Marconi in Western countries. The day marks the anniversary of Popov's presentation of a lightning detector, functioning as a radio receiver, to the Russian Physical and Chemical Society in 1895. Radio Day was first celebrated in the Soviet Union in 1925 and became an annual holiday in 1945, continuing in several former Soviet republics as a professional holiday for telecommunications professionals. Additionally, World Radio Day, proclaimed by UNESCO in 2011, is celebrated on February 13 each year.